// Package users is MyDay's user service: the stable person record, the role
// ladder, and the manager chain (PROJECT_PLAN.md §7, D-020/D-024/D-034).
//
// The user is the stable identity anchor; credentials hang off a rotating
// identity owned by the auth package (D-008). This package never touches
// credentials.
//
// Spec: docs/specs/spec-004-identity-sessions.md §3, §5.
package users

import (
	"context"
	"errors"
	"fmt"
	"time"
)

// Role is a user's single tier in the ladder admin > director > manager > team
// (D-034: one role per user, no ACL — the role ripples down).
type Role string

const (
	RoleAdmin    Role = "admin"
	RoleDirector Role = "director"
	RoleManager  Role = "manager"
	RoleTeam     Role = "team"
)

// roleRank orders the ladder. A higher number implies every lower role.
var roleRank = map[Role]int{
	RoleTeam:     1,
	RoleManager:  2,
	RoleDirector: 3,
	RoleAdmin:    4,
}

// Valid reports whether r is one of the four defined roles.
func (r Role) Valid() bool {
	_, ok := roleRank[r]
	return ok
}

// Rank returns the ladder position (higher = more authority); 0 for invalid.
func (r Role) Rank() int { return roleRank[r] }

// Above reports whether r is strictly higher than other on the ladder.
func (r Role) Above(other Role) bool { return r.Rank() > other.Rank() }

// String renders the role.
func (r Role) String() string { return string(r) }

// ParseRole validates a stored/entered role string.
func ParseRole(s string) (Role, error) {
	r := Role(s)
	if !r.Valid() {
		return "", fmt.Errorf("%w: %q", ErrInvalidRole, s)
	}
	return r, nil
}

// Optional carries a value that may be absent (Go has no nullable generics).
// It models the manager chain: the top admin has NO manager (D-021).
type Optional[T any] struct {
	Value T
	Set   bool
}

// Some returns a set Optional.
func Some[T any](v T) Optional[T] { return Optional[T]{Value: v, Set: true} }

// None returns an unset Optional.
func None[T any]() Optional[T] { return Optional[T]{} }

// UserID is the internal, stable person id. The first user is 1 (D-013).
type UserID = int64

// User statuses. A disabled user keeps their record and history but may not act.
const (
	StatusActive   = "active"
	StatusDisabled = "disabled"
)

// CanApprove reports whether approver may decide a recovery request for
// requester (SPEC-007 §4, ruling R-7). The authority is the CHAIN, not the
// ladder: the approver must be an ANCESTOR of the requester — on their manager
// line, upward — or the admin. The requester may never approve their own
// request (AC-2).
//
// approverIsAncestor is computed by the caller, which owns the chain lookup
// (users.Users.Manager); this predicate stays pure. A role merely *above* the
// requester is NOT sufficient — that was R-7's correction: an unrelated
// director must not be able to recover a team member outside their subtree.
func CanApprove(approver, requester User, approverIsAncestor bool) bool {
	if approver.ID == requester.ID {
		return false
	}
	if approver.Role == RoleAdmin {
		return true // the admin is the root of the chain and approves anyone (§4)
	}
	return approverIsAncestor
}

// User is the stable person record (SPEC-004 §4 `users`).
type User struct {
	ID          UserID
	Email       string
	DisplayName string
	Role        Role
	// Manager is the chain link: who approves this user (D-020). Unset only
	// for the top admin.
	Manager Optional[UserID]
	// PasskeyOptOut records that the user declined the passkey nudge (D-041).
	// It is a USER preference (not a credential), so it survives identity
	// rotation (D-008): an opted-out user is never re-nudged after recovery.
	PasskeyOptOut bool
	Status        string
	CreatedAt     time.Time
}

// Users is the service contract (SPEC-004 §5).
//
// Per ruling R-1 every method takes the request context: the door attaches
// audit.Meta (actor · client IP · correlation) before calling, and each
// mutation writes its audit row through it (A11).
type Users interface {
	// Create creates a user below the creator on the chain.
	//
	//   * creatorID != 0 — the creator must hold a role strictly ABOVE role
	//     (D-019/§7.3); the new user's manager defaults to the creator. A
	//     second admin is always rejected (AC-6).
	//   * creatorID == 0 — bootstrap: allowed ONLY while no user exists, and
	//     it must create the top admin (user 1, role admin, manager NULL).
	Create(ctx context.Context, creatorID int64, email, displayName string, role Role) (UserID int64, err error)

	// Get returns one user.
	Get(ctx context.Context, id int64) (User, error)

	// List returns every user, ordered by user_id (stable). It is the admin
	// Users page's read (SPEC-010 §5).
	List(ctx context.Context) ([]User, error)

	// SetRole changes a user's role (ripple-down model, D-034). It preserves
	// the one-admin invariant: only user 1 may be admin, and user 1 may not be
	// demoted (A14).
	SetRole(ctx context.Context, id int64, role Role) error

	// Manager returns the user above id in the chain.
	Manager(ctx context.Context, id int64) (Optional[UserID], error)

	// PasskeyOptOut reports whether the user has declined the passkey nudge
	// (D-041). The marker is a USER preference, so it survives identity
	// rotation.
	PasskeyOptOut(ctx context.Context, id int64) (bool, error)

	// SetPasskeyOptOut records the user's choice about the passkey nudge
	// (D-041) and audits it (A11).
	SetPasskeyOptOut(ctx context.Context, id int64, optOut bool) error
}

// Sentinel errors.
var (
	ErrNotFound        = errors.New("users: user not found")
	ErrInvalidRole     = errors.New("users: invalid role")
	ErrRoleNotAllowed  = errors.New("users: creator's role is not above the new user's role")
	ErrOneAdmin        = errors.New("users: exactly one admin is allowed")
	ErrTopAdmin        = errors.New("users: the top admin (user 1) cannot be demoted")
	ErrDuplicateEmail  = errors.New("users: email already in use")
	ErrEmailRequired   = errors.New("users: email is required")
	ErrNameRequired    = errors.New("users: display name is required")
	ErrBootstrapClosed = errors.New("users: bootstrap is only allowed while no users exist")
	ErrBootstrapAdmin  = errors.New("users: the bootstrap user must be the admin")
)